Outcomes research is a rapidly evolving field that incorporates epidemiology, health services research, health economics, and psychometrics. Measurement of clinical and other outcomes has become increasingly important to the stakeholders in a rapidly changing health care environment. The desire to improve outcomes and control costs has stimulated greater interest in cost-effectiveness studies, which determine how well effective therapies work in the usual practice setting and how much they cost. The application of outcomes principles to the practices of health care providers has resulted in efforts to implement disease management programs. Unlike traditional programs carried out by physicians, these new efforts are based on systematic population-based approaches to identifying persons at risk, intervening with specific programs of care, and measuring clinical and other outcomes. The new efforts depend heavily on modern information systems.